The present invention relates to a method of recovering elemental mercury from soils.
Elemental mercury is used in gold and silver mining operations to extract these precious metals from the ore. It is also extensively used in metering devices and pressure gauges in pump stations throughout the oil and gas industry, especially for gas and oil pipelines. Other applications include thermometers, switches, and rectifier tubes. Although the high toxicity of elemental mercury and other mercury compounds and their detrimental impact on the environment have been known for a long time, and some recovery processes and reclamation programs for mercury/mercury compounds have been investigated and are in use, a satisfactory, simple, and fast method of recovery has not been found.
Among the most common techniques used to date for mercury containing solid wastes are thermal recovery processes, such as retorting and roasting, acid leaching, stabilization of the solid waste, or incineration. The Environmental Protection Agency (EPA) has recommended thermal recovery processes such as retorting and roasting as the preferable methods (best demonstrated available technique--BDAT) for the recovery of elemental mercury from solid wastes (see Rules and Regulations published in the Federal Register, vol. 55, No. 106 (1990)). The greatest disadvantage of thermal processes, besides the relatively high energy expenditures, is the need for air emission control devices. Furthermore, the retorting and roasting facilities are stationary, immobile plants so that the mercury containing wastes or contaminated soils must be removed or excavated and shipped to the thermal processing plants.
It is therefore an object of the present invention to provide a method of removing mercury, especially elemental mercury, from contaminated soils which is highly effective and fast, does not pose any health hazards to the operating personnel and/or the environment, is simple and does not require expensive and elaborate equipment. Preferably, the method should be practicable with mobile and self-supporting equipment in order to be operable in remote areas that do not have access to municipal water and electricity.